Cast slip-ring assembly



March 31, 1964 J. 1.. RECTOR 3,126,596

CAST SLIP-RING ASSEMBLY Filed March 2, 1960 INVENTOR/ JfiCOfi 4. AZECTO United States Patent M 3,126,596 CAST SLIP-RING ASSEMBLY Jacob L. Rector, 27 lalisades Road, Linden, NJ. Fiied Mar. 2, H60, Ser. No. 12,419 4 Claims. (Cl. 22-202) The instant invention is directed to a slip-ring assembly construction, especially adapted for the sub-miniature size range, which is more reliable in operation than similar devices of the prior art and costs materially less to produce.

In the prior art, slip-ring assemblies were generally constructed either by placing conducting rings in a mold and then molding the insulating core or by forming an insulating core with grooves and thereafter filling the grooves with conducting material by an electro-plating process.

Slip-ring assemblies constructed according to the first recited method have the disadvantage that the conducting rings are not securely fastened to the core and as a result are not concentric with the axis of the core. The loose fitting between the rings and core is caused by the fact that the core material possesses a substantially greater coefficient of expansion than the material of which the rings are constructed.

A device constructed in accordance with the second method has the disadvantage that the device possesses a short shelf life since the electro-plating process requires extraneous means, that is, parts or chemicals for the electro-plating process which are not required for the final slip-ring assembly. The chemicals required for the electro-plating process often attack the core or rings and/ or leave residues to produce operational defects. These defects do not necessarily show up immediately upon manufacture and are expensive as well as time consuming to remove.

The instant invention overcomes the disadvantages of the prior art by providing a slip-ring assembly constructed by a process in which the insulating core is formed, placed in a suitable mold, and thereafter the slip-rings are cast in place. An assembly resulting from this process is especially advantageous in that the slip-rings, during the cooling thereof, shrink and thereby effectively clamp themselves to the core so as to remain concentric about the rotational axis of the core.

In addition, the process is such that the forming of the slip-rings is accompanied by simultaneously forming the connections between the external circuit Wires and the respective slip-rings. Further, the construction is such that a means is formed to prevent relative rotation between the core and slip rings and external circuit wires are not mechanically strained.

The preceding two features are accomplished by providing the core with longitudinal passages extending parallel to the rotational axis of the core and providing connecting passages between the longitudinal passages and the respective grooves which define the slip-rings. The stripped end of an insulation covered wire forming an external circuit connector is inserted in each of the longitudinal passages through first ends thereof. Thereafter molten conducting material is introduced through the other ends of the longitudinal passages with this material flowing through the longitudinal passage to a point where further flow through the passage is blocked by the conductor and its insulation cover. The molten metal then flows through the connecting passages into the circular grooves where the metal is confined by the mold. The metal may also be introduced directly to the annular grooves so that through longitudinal holes are not required. Variously shaped rings may be obtained, limited only by possible mold shapes.

Upon cooling of the assembly a metallurgical bond exists between each of the external circuit conductors and its associated slip-ring. The solidified metal in the con- $126,596 Patented Mar. 31, 1964 ducting passage forms a torque resisting pin to prevent rotation of the slip-ring relative to the core.

Accordingly, it is a primary object of the instant invention to provide a novel construction for a slip-ring assembly which is more reliable and more economical to produce than similar assemblies of the prior art.

Another object is to provide a slip-ring assembly in which the electrical connections between the slip-ring and external circuit conductors are formed simultaneously with the formation of the slip-rings and are integral therewith.

Still another object is to provide a novel process for the formation of a slip-ring assembly.

A further object is to provide an electrical device having an insulating core and conducting portions cast in place so as to be self-locked to the core.

These as well as other objects of the instant invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE 1 is a perspective view, many times enlarged, of a typical core forming part of a slip-ring assembly constructed in accordance with the teachings of the instant invention.

FIGURE 2 is a longitudinal cross-section of a complete slip-ring assembly taken through line 2-2 of FIG- URE 1.

FIGURE 3 is a longitudinal cross-section of a mold utilized in the process of forming the slip-ring assembly with the core and external circuit connectors in place just prior to pouring or injection of the metal. The section of the mold is taken through line 3-3 of FIGURE 4 looking in the direction of arrows 33.

FIGURE 4 is an end view of the mold of FIGURE 3 looking in the direction of arrows 44 of FIGURE 3.

Now referring to the figures, slip-ring assembly 10 includes core 15 of insulating material such as Teflon, transite, ceramic or plastic. Core 15 comprises an elongated cylindrical body having a plurality of longitudinally spaced annular grooves 16-19 formed in the outer surface thereof. Longitudinal opening Ztl extending through core 15 defines an axis of rotation for core 15 and is adapted to receive a supporting shaft (not shown). Annular grooves 16-19 in the periphery of core 15 are formed concentric with opening 29.

Core 15 also includes a plurality of passages 2225 extending longitudinally therethrough with each of the passages 22-25 being connected to an individual one of the grooves 16-19 by means of radially extending connecting passages 2629, for reasons to be hereinafter explained.

Insulation cover conductors Fail-33 for external circuit connections are inserted into individual ones of the longitudinal passages 2225 at the left end of assembly 10, with respect to FIGURE 2. The ends of conductors ltd-33 are stripped and are metallurgically bonded to the conducting material 40, such as silver which occupies longitudinal passages 30-33. Material 40 also occupies connecting passages 2629 and extends into grooves 1649 to form slip rings 4245. The portion of material 40 in each of the connecting passages 26-29 forms a stem which prevents relative rotation between rings 42-45 and core 15.

Slip-ring assembly ltl is constructed by inserting core 15 and external circuit conductors 3043 mounted thereto into mold 5i). Mold 50 includes a cylindrical bore 51 extending from end 5 2 to a point in mold 50 where bore 51 is joined by four radially extending vents 53-56. Pouring passage 5'7 extends from mold end 58 to bore 51 with pouring passage 57 having a tapered mouth 59. The mold is then placed in a vertical position with the wide mouth 59 facing upwardly.

Conducting material in molten form is then poured into mouth 59, flowing through passage 57 into the space 60 between core end 49 and the upper end of bore 51. The molten material 40 then flows into longitudinal passages 22-25 through connecting passages 26-29 into grooves 16-19. The close fit between the insulation of conductors 30-33 and passages 22-25 prevents material 40 from flowing out the lower ends of these passages. The outer diameter of core is closely fitted to bore 51 so that mold 50 effectively confines material introduced into grooves 1619. Upon cooling of material 40 it is metallurgically bonded to conductors 30-33 at the stripped ends thereof.

It the amount of material introduced through passage 57 is not closely controlled there may be an excess formed over bore surface 49. After removal of core 15 from mold 50 this excess material is removed as by grinding. In some cases machining is required for rings 42-45 to apply a smooth finish thereto. V-shaped groove 48, when desired, may be machined in slip-rings 42-45. Grooves 48 serve as a guide means for brushes (not shown) which are adapted to contact slip-rings 42-45 in a manner well known to the art.

Grooves 48 may be formed in the casting process by providing mold 50 with suitable formations extending into bore 52. In this event, mold 50 would be constructed of resilient material or else be constructed of a number of interlocked pieces.

Thus, I have provided a novel construction for a slip-ring assembly wherein the slip-rings are cast in place after fabrication of the insulating core. With this construction connections to the external circuit conductors are made simultaneously with the formation of the slipring.

While my invention has hereinbefore been described as including a grooved core to receive and confine the material forming the slip-rings it is to be understood that these grooves are not absolutely necessary. That is, the metal slip-rings may reside entirely on the outer surface of the core by having the mold provided with suitable grooves to confine the ring material.

While only a slip-ring construction has been illustrated and hereinbefore described, it should be further understood that this invention is not limited to slip-ring constructions but may include commutators and other means for transmitting electrical energy and signals between two relatively moving members.

Although I have here described preferred embodiment of my novel invention, may variations and modifications will now be apparent to those skilled in the art, and I therefore prefer to be limited, not by the specific disclosure herein, but only by the appending claims.

I claim:

1. A method of forming a slip-ring assembly comprising the step of constructing a cylindrical insulating core having a plurality of longitudinally spaced concentric peripheral ring grooves, a plurality of longitudinal passages extending therethrough, one for each of said grooves, and a connecting passage between each of said grooves and its associated longitudinal passage; inserting a conductor into each of said longitudinal passages through first ends thereof: placing said core in a suitable mold for confining material introduced into said grooves; introducing molten conducting material into said longitudinal passages through second ends thereof in a quantity sufficient to occupy said connecting passages, said grooves and portions of said longitudinal passages not occupied by said conductors; cooling said molten conducting material until it solidifies.

2. A method of forming a slip-ring assembly comprising the steps of constructing a cylindrical insulating core having a plurality of longitudinally spaced concentric peripheral ring grooves, a plurality of longitudinal passages extending therethrough, one for each of said grooves, and a connecting passage between each of said grooves and its associated longitudinal passage; inserting a conductor into each of said longitudinal passages through first ends thereof; placing said core in a suitable mold for confining material introduced into said grooves; introducing molten conducting material into said longitudinal passages through second ends thereof in a quantity sulficient to occupy said connecting passages, said grooves and portions of said longitudinal passages not occupied by said conductors; cooling said molten conducting material until it solidifies, removing said core from said mold; removing excess solidified conducting material from said core immediately adjacent to said longitudinal passages second ends until the material in each of said longitudinal passages is electrically insulated from the material in the others of said longitudinal passages.

3. A method of forming a slip-ring assembly comprising the steps of constructing a cylindrical insulating core having a plurality of longitudinally spaced concentric peripheral ring grooves, a plurality of longitudinal passages extending therethrough, one for each of said grooves, and a connecting passage between each of said grooves and its associated longitudinal passage; inserting the stripped end of an insulation cover conductor into each of said longitudinal passages through first ends thereof at least to a point where said longitudinal passages are closed off by said conductor insulation, said point being such that said conductor insulation does not extend beyond the points where said connecting passages meet their associated longitudinal passages; placing said core in a suitable mold for confining material introduced into said grooves; introducing molten conducting material into said longitudinal passages through second ends thereof in a quantity suflicient to occupy said connecting passages, said grooves and portions of said longitudinal passages not occupied by said conductors, cooling said molten conducting material until it solidifies.

4. A method of forming a slip-ring assembly comprising the steps of constructing a cylindrical insulating core having a plurality of longitudinally spaced concentric peripheral ring grooves, a plurality of longitudinal passages extending therethrough, one for each of said grooves, and a connecting passage between each of said grooves and its associated longitudinal passage; inserting the stripped end of an insulation cover conductor into each of said longitudinal passages through first ends thereof at least to a point where said longitudinal passages are closed off by said conductor insulation, said point being such that said conductor insulation does not extend beyond the points where said connecting passages meet their associated longitudinal passages; placing said core in a suitable mold for confining material introduced into said grooves; introducing molten conducting material into said longitudinal passages through second ends thereof in a quantity sufiicient to occupy said connecting passages, said grooves and portions of said longitudinal passages not occupied by said conductors, cooling said molten conducting material until it solidifies, removing said core from said mold; removing excess solidified conducting material from said core immediately adjacent to said longitudinal passages second ends until the material in each of said longitudinal passages is electrically insulated from the material in the others of said longitudinal passages.

References Cited in the file of this patent UNITED STATES PATENTS 1,782,447 Scranton Nov. 25, 1930 2,004,784 Evans June 11, 1935 2,192,787 Elsey Mar. 5, 1940 2,252,371 Greenhow et al Aug. 12, 1941 2,473,526 Hood et al June 21, 1949 2,696,570 Pandapas Dec. 7, 1954 FOREIGN PATENTS 553,044 Great Britain May 5, 1943 

1. A METHOD OF FORMING A SLIP-RING ASSEMBLY COMPRISING THE STEP OF CONSTRUCTING A CYLINDRICAL INSULATING CORE HAVING A PLURALITY OF LONGITUDINALLY SPACED CONCENTRIC PERIPHERAL RING GROOVES, A PLURALITY OF LONGITUDINAL PASSAGES EXTENDING THERETHROUGH, ONE FOR EACH OF SAID GROOVES, AND A CONNECTING PASSAGE BETWEEN EACH OF SAID GROOVES AND ITS ASSOCIATED LONGITUDINAL PASSAGE; INSERTING A CONDUCTOR INTO EACH OF SAID LONGITUDINAL PASSAGES THROUGH FIRST ENDS THEREOF; PLACING SAID CORE IN A SUITABLE MOLD FOR CONFINING MATERIAL INTRODUCED INTO SAID GROOVES; INTRODUCING MOLTEN CONDUCTING MATERIAL INTO SAID LONGITUDINAL PASSAGES THROUGH SECOND ENDS THEREOF IN A QUANTITY SUFFICIENT TO OCCUPY SAID CONNECTING PASSAGES, SAID GROOVES AND PORTIONS OF SAID LONGITUDINAL PASSAGES NOT OCCUPIED BY SAID CONDUCTORS; COOLING SAID MOLTEN CONDUCTING MATERIAL UNTIL IT SOLIDIFIES. 